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Data Set ID:

G10006

Unified Sea Ice Thickness Climate Data Record, 1947 Onward, Version 1

The Unified Sea Ice Thickness Climate Data Record, 1947 Onward is the result of a concerted effort to collect as many observations as possible of Arctic and Antarctic sea ice draft, freeboard, and thickness and to format them consistently with clear documentation, allowing the scientific community to better utilize what is now a considerable body of observations.

In September 2013, the official archive for this data set was transferred from the Polar Science Center to NSIDC. However, the original Unified Sea Ice Thickness Climate Data Record web site, at the University of Washington, is still active and may contain more recent data than what is housed at NSIDC. If the latest data have not been added to this archive, yet, please visit the original Unified Sea Ice Thickness Climate Data Record web site for access to those data.

Overview

This data set provides a collection of observations of sea ice from 1947 onward. It is the result of a concerted effort to collect as many observations as possible of Arctic and Antarctic sea ice draft, freeboard, and thickness and to format them consistently with clear documentation, allowing the scientific community to better utilize what is now a considerable body of observations. The Unified Arctic Sea Ice Thickness Climate Data Record includes data from moored and submarine-based upward looking sonar (ULS) instruments, airborne electromagnetic (EM) induction instruments, satellite laser altimeters (ICESat), and airborne laser altimeters (IceBridge). These instruments offer adequate sampling, starting in 1975, to establish the mean Arctic sea-ice thickness and the sea-ice thickness distribution at scales generally appropriate for change detection and climate model validation. The Unified Sea Ice Thickness Climate Data Record consists of over 15 different data sets. Each data set consists of a Summary file and a Distribution file. The majority of the data in this data set are for the Arctic with a small portion covering the Antarctic but is open to accepting more Antarctic data.

This document contains general information common to all the data sets, as well as specific information about each data set, and access to all the Summary and Distribution files. The metadata for each data set includes pointers to the original source data. For the complete list of all data sets see Table 1 for a summary or the Data Acquisition and Processing section for complete details.

History of Product Development

While sea ice extent is well measured by satellites, measuring sea ice thickness remains a challenge. However, the amount of sea ice draft and sea ice freeboard data available from both polar regions has increased markedly, providing a large and growing resource. Existing observations of sea ice thickness span a variety of methods, accuracies, and temporal and spatial scales and are archived in a variety of different locations and in different formats. Each data source has its own strengths in terms of sampling or accuracy. The uncertainties are documented to various levels of detail for the different data sources but the documentation in general is spread throughout the literature.

This effort was funded by a grant from the NOAA Climate Program Office (from 2009 to 2013) to R.W. Lindsay at the Polar Science Center, University of Washington, Seattle to create a climate data record of sea ice thickness. A climate data record is "a time series of measurements of sufficient length, consistency, and continuity to determine climate variability and change" (NRC, 2004). Lindsay collected all the data, divided it into monthly or 50 km aggregates, calculated the statistics, formatted the output, posted the products on a web site, and wrote the documentation. An article describing the project was published in Eos:

In September 2013, the data set and documentation for the Unified Sea Ice Thickness Climate Data Record were transitioned from the Polar Science Center to NSIDC. The original Unified Sea Ice Thickness Climate Data Record web site, at the University of Washington, is still active.

If you have data on sea-ice draft, freeboard, or thickness that you would like to contribute to the Unified Sea Ice Thickness Climate Data Record, please contact one of the investigators listed at the end of this document in the Contacts and Acknowledgments section of this document.

Detailed Data Description

All data records are based on either a calendar month (for moorings) or on a region approximately 50 km in diameter (for submarine, airborne, or satellite data). Each one-month or 50 km aggregate represents a variable number of point measurements, depending on the measurement system and the specific sampling.

The Summary files contain monthly averages of moored ULS data or 50 km averages of submarine, airborne, or satellite data. Roughly 50 km of sea ice passes over a typical mooring site in a month, and monthly output is commonly saved in computer model runs. The Summary files also include the minimum, maximum, and standard deviation of the data in each one-month or 50 km aggregate. All Summary files are in the same ASCII text format.

The Distribution files are based on the same data that go into the Summary files. They consist of the fractional number of samples in each bin of sea ice draft or thickness. There are 300 bins of width 10 cm each, centered at 0, 10, 20, 30, ... 2990 cm. The first bin, centered at 0 cm, is for the open water fraction. All Distribution files are in the same ASCII text format.

One data set in this collection contains sea ice thickness measurements prior to 1975: the Ice Thickness Program run by Environment Canada, known here as CanCoast. Point measurements of sea ice thickness on landfast ice at coastal stations in the Canadian Arctic Archipelago began in 1947. The program peaked during the years 1959-1991. Since only a few measurements were made each month at each station, no thickness distributions were calculated and hence there is no Distribution file.

Finally, a number of the data sets in this collection report sea ice draft. In order to convert sea ice draft into thickness, assumptions must be made about the density of sea ice and the density and depth of the snow on the sea ice. Only one data set (CanCoast) contains direct measurements of sea ice thickness and snow depth. The Airborne EM (Air-EM) data set measures the combined snow-plus-ice thickness. ICESat measures sea ice freeboard and then sea ice thickness is computed by the data set provider based on assumptions about snow depth and density. IceBridge aircraft measure sea ice freeboard and snow depth, and the IceBridge project derives sea ice thickness from them. Converting all data sets into consistent estimates of sea ice thickness is not a straightforward task, due in part to uncertainties in estimates of the depth and density of snow on sea ice. When a data set does not report sea ice thickness, the conversion to thickness is left to the user.

Table 1 lists the data set number and data set name, the years for which data are available, and the general location of the data. The Records column contains the number of lines in the Summary and Distribution files, excluding the initial one-line header. The Parameter/instrument column gives the primary parameter in the data set (draft or thickness) and the type of instrument that measured it. The Summary Variables column gives the three variables in the Summary file. Note: The third summary variable is always the primary variable of the data set.

Table 1. Data Sets Used in this Unified Sea Ice Thickness CDR

Data Set #

Short Name

Long Name

Years

Location

Records

Parameter/instrument

Summary Variables (See Table 2 for description of each variable)

1

NPEO

North Pole Environmental Observatory

2001 - 2010

North Pole

64

Draft / moored ULS

Temperature, Depth, Draft

2

BGEP

Beaufort Gyre Exploration Project

2003 - 2013

Beaufort Sea

371

Draft / moored ULS

Temperature, Depth, Draft

3

IOS-EBS

Institute of Ocean Sciences - Eastern Beaufort Sea

1990 - 2003

Eastern Beaufort Sea

382

Draft / moored ULS

Temperature, Depth, Draft

4

IOS-CHK

Institute of Ocean Sciences - Chukchi Sea

2003 - 2005

Chukchi Sea

26

Draft / moored ULS

Temperature, Depth, Draft

5

US-Subs-AN

US Navy Submarines - Analog

1960 - 2005

Arctic Ocean

844

Draft / submarine ULS

None, Depth, Draft

6

US-Subs-DG

US Navy Submarines - Digital

1986 - 1999

Arctic Ocean

1001

Draft / submarine ULS

None, None, Draft

7

UK-Subs-AN

UK Navy Submarines - Analog

1987 and 1991

Arctic Ocean

149

Draft / submarine ULS

None, None, Draft

8

UK-Subs-DG

UK Navy Submarines - Digital

1976

Arctic Ocean

27

Draft / submarine ULS

None, None, Draft

9

AWI-GS

Alfred Wegener Institute - Greenland Sea

1991 - 2002

Greenland Sea

134

Draft / moored ULS

Temperature, Depth, Draft

10

Air-EM

Airborne Electromagnetic Induction

1991 - 2002

Arctic Ocean

134

Ice + Snow thickness / aircraft EM

None, Height, Ice+Snow Thickness

11

ICESat1-G

NASA ICESat Mission - Goddard

2003 - 2008

Arctic Ocean

29452

Thickness / sat. laser altimeter

None, Freeboard, Thickness

12

BIO-LS

Bedford Institute of Oceanography Lancaster Sound

2003 - 2007

Lancaster Sound

36

Draft / moored ULS

Temperature, Depth, Draft

13

CanCoast

Environment Canada

1947 - 2013

Canadian Archipelago, coastal stations

6242

Thickness / bore holes

None, Snow, Thickness

14

Davis_St

Polar Science Center - DS

2005 - 2008

Davis Strait

67

Draft / moored ULS

Temperature, Depth, Draft

15

IceBridge-V2

NASA Operation IceBridge V2

2009 - 2013

Arctic Ocean

933

Thickness / air. laser altimeter

Snow, Uncertainty, Thickness

16

IceBridge-QL

NASA Operation IceBridge Quick Look

2012 - 2016

Arcitc Ocean

882

Thickness / air. laser altimeter

Snow, Uncertainty, Thickness

17

CryoSat-AWI

European Space Agency CryoSat satellite - Alfred Wegener Institute

2011 - 2017

Arctic Ocean

141714

Freeboard / radar altimeter

Uncertainy, Uncertainy, Thickness

18

ICESAT1-SH

NASA ICESat Mission - Southern Hemisphere

2003 - 2008

Southern Ocean

12432

Thickness / sat. laser altimeter

None, Freeboard, Thickness

19

AWI-WS

Alfred Wegener Institute - Weddell Sea

1990 - 2010

Weddell Sea

757

Draft / moored ULS

Temperature, Depth, Draft

Table 2. Description of Summary Variables from Table 1.

Summary Variable

Abbreviation used in
Summary Files1

Description (units)

Temperature

Temp

Water temperature (°C)

Depth

Depth

Instrument depth (meters)

Draft

Draft

Sea-ice draft (meters)

Height

Hight

Instrument height (meters)

Ice+Snow Thickness

Ic+sn

Sea-ice thickness plus snow depth (meters)

Thickness

Thkns

Sea-ice thickness (meters)

Freeboard

Frbrd

Sea-ice freeboard (meters)

Snow

Snow

Snow depth (meters)

Uncertainty

Uncert

Sea-ice thickness uncertainty (meters)
(Note for the CryoSat-AWI there are two uncertainties both labeled uncertainty. The first is random uncertainty and the second is systematic uncertainty.)

1In the actual Summary Files, these abbreviations are prepended by either Avg_, Min_, Max_, or SD_.

In addition, a complete listing of dates and specific geographic locations of each individual data set used is available in the following file: sea_ice_CDR_data_set_overview_v1.1.txt. Table 3 describes the columns of that file.

Table 3. Description of the Columns in sea_ice_CDR_data_set_overview_v1.1.txt

Column

Description

DSN

Data set number

DataSet

Data set name

Platform

Lists an abbreviation for the instrument used for each data set.

For the ULS moorings, the platform name indicates the instrument. For example, for data set #1 (NPEO), NPEO-2001 indicates the ULS instrument that was put in place in 2001; NPEO-2002 indicates the instrument that was put in place in 2002, etc.

For submarine data, the platform name indicates a different cruise by year.

For Air-EM, the platform is the "Campaign". Different campaigns are different sets of flights. For example, the aircraft might be based at a certain location and make several flights from there. That would be one campaign. Later, the plane is based at another location and makes another set of flights. That is considered another campaign.

For ICESat1-G, the platform (campaign) indicates which lasers were used.

For CanCoast, the platform is the station where the measurements were made.

For IceBridge, the platform is the campaign (like Air-EM, IceBridge is aircraft flights).

Number of point observations that went into the aggregated values given in the Summary and Distribution files.

Nagr

Number of aggregated values given in the Summary and Distribution files. The total of "Nagr" for a given data set is the number of Records given in Table 1 for that data set.

Format

Summary Files

Each Summary file is in ASCII plain text format. The first line of the file is a header identifying the variables, which are listed in Table 4. Subsequent lines of the file are the values of the variables for each one-month or 50 km aggregate. The number of data lines in each file is given in Table 1 in the column labeled Records.

The first 16 fields of each row in a Summary file, except the initial header row, contain the location, time, and other identifying information about the data. The last 12 fields of each row contain the average, minimum, maximum, and standard deviation of up to three variables. See Table 1 (last column) for a list of these three variables by file name. The values of these variables are computed from the underlying point measurements over a calendar month (for moorings) or over a region approximately 50 km in diameter (for other data sets). For example, in the North Pole Environmental Observatory (NPEO) summary data file, the three variables in the file are water temperature, instrument depth, and sea ice draft. So, the last four fields in each line of this file are the average, minimum, maximum, and standard deviation of sea ice draft over the one-month period given by the Month field in the year given by the Year field.

A value of -999 indicates a missing value where the data are not applicable or not available.

Distribution Files

Each Distribution file is in ASCII plain text format. The first line of the file is a header identifying the variables, which are listed in Table 5. Subsequent lines of the file are the values of the variables for each one-month or 50 km aggregate, depending on the file. The number of lines in each file is given in Table 1 in the column labeled Records.

The first 19 fields of each row in a Distribution file, except the initial header line, contain the location, time, and other identifying information about the data. The first 16 of these are the same information as is found in the first 16 fields of the Summary files. After the first 19 fields, the Distribution file contains the probability density function (PDF) of either sea ice draft or sea ice thickness, depending on the data set. For example, the Distribution file for the NPEO data set contains the PDF of sea ice draft. The PDF constitutes the last 300 fields of each row. The PDF is based on the same one-month or 50 km aggregate of data as in the Summary file. The PDF consists of the fractional number of data values in each of 300 bins. The bins are 10 cm wide, and they are centered at 0 cm, 10 cm, 20 cm, 30 cm, ... 2990 cm. The first bin, centered at 0 cm, is for the open water fraction.

Note: The the UK submarine analog files contain an "and" in the file name to distinguish that this file only contains two years of data instead of a range like the other files do.

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File Size

See Table 1 for the number of records in each Summary and Distribution file. The size of each Summary file is 255 bytes × (number of records + 1). The size of each Distribution file is 2255 bytes × (number of records) + 154.

The zipped data file is 14 MB and the total volume is 146 MB unzipped.

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Spatial Coverage and Resolution

For the moored ULS data sets, the spatial coverage is just a single point. See the Summary file or the Distribution file for the latitude and longitude of the instrument.

For other data sets, the underlying data have been grouped into regions approximately 50 km in diameter before computing the statistics in the Summary file and the probability density function in the Distribution file. The mean latitude and longitude of the underlying data in each 50 km region are given in both the Summary and the Distribution files, as are the minimum and maximum latitude and longitude. For a complete list of the geographic locations, see the sea_ice_CDR_data_set_overview_v1.1.txt file.

Figure 1. Left panel: Locations of all submarine observations. Right panel: Locations of moored (green), airborne (red), and coastal (blue) observations. ICESat observations (2005-2007) are not shown because their coverage includes the entire Arctic Ocean up to 86° N. Note: These figures have not been updated since 2013. Click for larger view.

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Temporal Coverage

The temporal coverage varies depending on the data set but the unified CDR begins in 1947 and goes through most recent processing. The mooring data have been grouped into calendar months before computing the statistics in the Summary file and the probability density function in the Distribution file. Each line (record) of the Summary and Distribution files contains the month and year for that record, as well as the mean day-of-year of the data for that month. The years spanned by the data are given in Table 1, but not every month of the entire span contains data - there are some gaps. See the Summary or Distribution files for the exact months and years of coverage. For a complete list of the dates, see the sea_ice_CDR_data_set_overview_v1.1.txt file.

Figure 2.Temporal distribution of the aggregate observations from 1970 to 2012. Note: This figure has not been updated since 2013. Click for larger view.

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Parameters

The parameters of this data collection are sea ice draft, sea ice thickness, and sea-ice-plus-snow thickness, depending on the data set. Ice draft is a measurement of the thickness of the sea ice below the waterline and often serves as a close proxy for total ice thickness. Note that draft, thickness, and sea-ice-plus-snow measurements are not available for the entire temporal coverage. Other Summary variables may also include water temperature, instrument depth or height, sea ice freeboard, snow depth, or sea ice thickness uncertainty. See Table 1 for a listing.

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Software and Tools

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Data Acquisition and Processing

This unified sea ice thickness data set was compiled from the sources described below.

Data Processing Notes
ULS data were processed and calibrated by R. Moritz. The ULS instruments were manufactured by the Applied Physics Laboratory, University of Washington. Statistical summaries were computed and reformatted by R. Lindsay from the point data. Additional details on the ULS instruments and calibration procedures are presented in Drucker et al. (2003). All of the NPEO ULS data through 2012 are included in this data set.

"The data were collected and made available by the Beaufort Gyre Exploration Project based at the Woods Hole Oceanographic Institution." If you use these data, please provide us with a citation to include in our compilation of publications. Send to Andrey Proshutinsky aproshutinsky@whoi.edu and Rick Krishfield rkrishfield@whoi.edu.

National Science Foundation: The BGEP project is funded by the Office of Polar Programs grant numbers ARC-0230184, ARC-0424824, ARC-0532754, ARC-063399, ARC-0631951, ARC-0722694, ARC-0806115, ARC-0938137. Woods Hole Oceanographic Institution: WHOI is a private, nonprofit research facility dedicated to the study of marine science. Support to continue the BGEP field program for a second year was provided by the Ocean and Climate Change Institute.

Data Processing Notes
Data were processed and calibrated by R. Kirshfield, WHOI. The ULS instruments were manufactured by ASL Environmental Sciences. Statistical summaries were computed from the 2-second data by R. Lindsay, PSC. After 2008, significant new processing steps were required at WHOI to account for extensive open water seen during some periods. All available data through August 2011 are included.

Distribution of the data set from NSIDC is supported by funding from NOAA's National Environmental Satellite, Data, and Information Service (NESDIS) and the National Geophysical Data Center (NGDC).

Data Processing Notes
Data were processed and calibrated by H. Melling and D. A Reidel, IOS. The ULS instruments were manufactured by ASL Environmental Sciences. Monthly statistical summaries were computed by IOS and reformatted by R. Lindsay. The NSIDC data set has 10 observation sites, but the tenth has ice velocity data only.

The mooring is a collaborative undertaking of the Canadian Institute of Ocean Sciences, the USA Cold Regions Research Engineering Laboratory and the NOAA Arctic Research Office. The effort is jointly supported by NOAA Climate Program Office and the Canadian Department of Fisheries and Oceans.

Data Processing Notes
Data were processed and calibrated by H. Melling and D. A Reidel, IOS. The ULS instruments were manufactured by ASL Environmental Sciences. Statistical summaries were computed by IOS and reformatted by R. Lindsay, PSC. The summaries here are from the point data, not the distributions corrected for ice motion (the so-called pseudo-spatial data sets that are also available).

The U.S. analog data were processed at the Polar Science Center at the University of Washington and provided with documentation by M. Wensnahan and D. A. Rothrock. These data were prepared with funding from NSF Office of Polar Programs.
From the NSIDC documentation: “Researchers making use of these invaluable data owe a debt of gratitude to the present and past staff of the Arctic Submarine Laboratory, San Diego, California.”

Data Processing Notes
The point data have been averaged for clusters that fall within 50-km diameter circles, so where the submarine has turned or crossed back over its track, more than 50-km of track length is used for a single average distribution. All of the submarine data archived at NSIDC are included here.

The U.S. digital data were processed at the Polar Science Center at the University of Washington and provided with documentation by M. Wensnahan and D. A. Rothrock. These data were prepared with funding from NSF Office of Polar Programs.
From the NSIDC documentation: “Researchers making use of these invaluable data owe a debt of gratitude to the present and past staff of the Arctic Submarine Laboratory, San Diego, California.”

Preparation of the U.K. data was funded by a subcontract under a National Science Foundation Office of Polar Programs project "Analysis of Arctic Ice Draft Profiles Obtained by Submarines." The data were processed by the Department of Applied Mathematics and Theoretical Physics, University of Cambridge, with the cooperation of the Royal Navy and the U.K. Hydrographic Office. N.R Davis and P. Wadhams were involved in the production of the U.K. data.

Data Processing Notes
The point data at NSIDC for 50-km segments (which are interpolated to 1-m samples and gaps are interpolated) were summarized by R. Lindsay. Segments with a length of less than 25 km were dropped.

Preparation of the U.K. data was funded by a subcontract under a National Science Foundation Office of Polar Programs project "Analysis of Arctic Ice Draft Profiles Obtained by Submarines." The data were processed by the Department of Applied Mathematics and Theoretical Physics, University of Cambridge, with the cooperation of the Royal Navy and the U.K. Hydrographic Office. N.R Davis and P. Wadhams were involved in the production of the U.K. data.

Data Processing Notes
Data were processed and calibrated by AWI. The ULS instruments were manufactured by the Applied Physics Laboratory, University of Washington. The data processed here were obtained from the NSIDC archives. Statistical summaries were computed by R. Lindsay, PSC, from the 5-minute point data.

Dr. Dierking notes that one problem with the data sets available at NSIDC is that a bias factor was applied to account for the width of the sonar beam. However, only an approximate average value was used that was based on a limited comparison of ice thickness values derived from the ULS and those obtained from drilling. Since we think that such a value is not generally valid we decided not to include such a bias correction in our future data sets, leaving the choice of handling this problem to the end-user. This is the only ULS data set for which an unknown constant correction was applied to account for beam width and first-return bias.

Methodology
Airborne electromagnetic induction measures snow + ice thickness. EM sounding is a classical geophysical method to detect the distance between an EM instrument and the boundary between the resistive sea ice and the conductive seawater, in other words, its altitude above the ice/water-interface. The method is based on measurements of the amplitude and phase of a secondary EM field induced in the seawater by a primary field transmitted by the EM instrument. Surveys are usually performed with a towed sensor package, which is operated some tens of meters below the aircraft and 20 m above the ice. The instrument's altitude above the snow or ice surface is measured with a laser altimeter. Ice-plus-snow thickness results from the difference between the altitude above the ice/water-interface and above the snow or ice surface [Haas et al., 2009]. The accuracy of EM measurements is ±0.1 m over level ice [Pfaffling et al., 2007; Haas et al., 2009]. However, the maximum thickness of pressure ridges is generally underestimated due to their porosity and the EM footprint diameter of up to 3.7 times the instrument altitude [Reid et al., 2006]. The measured thickness of unconsolidated ridges can be less than 50% of the "true" thickness (Haas and Jochmann, 2003). Therefore, the measured thickness distributions are most accurate with respect to their modal thickness, while mean ice thickness can still be used for relative comparisons between regions and campaigns.

Data Processing Notes
Data were processed and calibrated by Dr. Haas and Dr. Hendricks. Statistical summaries and distributions for 50-km clusters were computed by R. Lindsay from the point data. Where the tracks overlap or bend, more than 50 km of track is included in many clusters. When flights spanned a few days in a small region, the flights were combined when the clusters were formed.

Data Processing Notes
This data set provides measurements of sea-ice freeboard and sea-ice thickness for the Arctic Ocean. The data were acquired from the Ice, Cloud, and land Elevation Satellite (ICESat) Geoscience Laser Altimeter System (GLAS) instrument, the Special Sensor Microwave/Imager (SSM/I), and climatologies of snow and drift of ice. The data span six GLAS campaigns, laser 3D through 3I, from 21 October 2005 to 05 November 2007. Data parameters include sea-ice freeboard and thickness derived from GLAS Release 28 data. The data at NSIDC are provided in three formats: ASCII track data, 25-km gridded polar stereographic data, and Portable Network Graphic (PNG) image files. The ASCII track data of position and ice thickness have a resolution of about 170 meters in the along-track direction. For this data set the track data for each entire laser campaign have been averaged for clusters that fall within 50-km grid cells. Summary statistics and probability density functions of sea-ice thickness are included here. At least 500 point values are required within a grid cell for the summary to be retained.

Methodology
Weekly bore holes or hotwire thickness gauges were used to measure the thickness of specific locations on fast ice. This data collection contains ice thickness and snow depth measurements for sites going back as far as 1947 for the first stations established in the Canadian Arctic (Eureka and Resolute). Record length varies from station to station. Most of the data in the current archive at Environment Canada's Canadian Ice Service (CIS) have been collected by Environment Canada's Meteorological Service, but some data are provided by other organizations such as the St. Lawrence Seaway Authority, Trent University, and Queen's University.

Measurements are taken at approximately the same location every year on a weekly basis, starting after freeze-up when the ice is safe to walk on, and continuing until break-up or when the ice becomes unsafe. The location is selected close to shore, but over a depth of water which will exceed the maximum ice thickness. Ice thickness is measured to the nearest centimeter using either a special auger kit or a hot wire ice thickness gauge. The depth of snow on the ice at the location of the ice thickness measurement is also measured and reported to the nearest centimeter. Measurements after 1982 include additional information such as the character of the ice surface, water features and method of observation.

Data Processing Notes
Monthly summaries of snow depth and sea-ice thickness were computed by R. Lindsay for each station. There were usually just three or four observations per month. No distributions were computed since there were so few observations per month.

The following table gives the station names for each identifier, the start and end years, and the location.

Data Processing Notes
Data were processed and calibrated by R. Moritz. The ULS instruments were manufactured by the Applied Physics Laboratory, University of Washington. Statistical summaries were computed and reformatted by R. Lindsay from the point data. Additional details on the ULS instrument and calibration procedures are presented in Drucker et al. (2003).

Data Processing Notes
All flights with usable data are combined for each campaign. Annual campaigns are conducted in the appropriate spring based either in Greenaland or Punta Arenas, Chile.

The 'Freeboard, Snow Depth, and Ice Thickness' data product from NSIDC was used to form 50-km clusters, combining data from more than one flight if the flights were less than 10 days apart. The spacing of the point thickness estimates is approximately 25 m. The original data set includes a variable for the uncertainty in the estimated ice thickness that is used to select points with an uncertainty of less than 1 m for very thin ice up to 2 m for ice greater than 4 m thick. The maximum uncertainty in the point measurements included in the clusters is 2 m. Clusters were required to have 500 or more point samples to be retained and some clusters have as many as 7000 points. The average is 1670 points.

In the summary file the minimum, maximum, mean, and standard deviation is given for the snow depth, the uncertainty in the ice thickness, and the ice thickness. See the file headers. The mean uncertainty is not the uncertainty of the mean because we do not know how the errors are correlated, but it does give some information about the relative confidence in the sample estimates. If the errors were uncorrelated the uncertaity in the mean would be approximately 1/sqrt(nsamps) times the mean uncertainty. The 20-m point data for ice thickness is at the National Snow and Ice Data Center as well as all of the calibrated instrument data.

Data Processing Notes
This is the Quicklook Product. SInce IceBridge data processing typically lags about a year this Quicklook Product is provided. Overlap between 2012 and 2013 V2 products provides some indication of potential differences though those may vary from year to year.

All flights with usable data are combined for each campaign. Annual campaigns are conducted in the appropriate spring based either in Greenaland or Punta Arenas, Chile..

The 'Freeboard, Snow Depth, and Ice Thickness' data product from NSIDC was used to form 50-km clusters, combining data from more than one flight if the flights were less than 10 days apart. The spacing of the point thickness estimates is approximately 25 m. The original data set includes a variable for the uncertainty in the estimated ice thickness that is used to select points with an uncertainty of less than 1 m for very thin ice up to 2 m for ice greater than 4 m thick. The maximum uncertainty in the point measurements included in the clusters is 2 m. Clusters were required to have 500 or more point samples to be retained and some clusters have as many as 7000 points. The average is 1670 points.

In the summary file the minimum, maximum, mean, and standard deviation is given for the snow depth, the uncertainty in the ice thickness, and the ice thickness. See the file headers. The mean uncertainty is not the uncertainty of the mean because we do not know how the errors are correlated, but it does give some information about the relative confidence in the sample estimates. If the errors were uncorrelated the uncertainty in the mean would be approximately 1/sqrt(nsamps) times the mean uncertainty. The 20-m point data for ice thickness is at the National Snow and Ice Data Center as well as all of the calibrated instrument data.

Data Processing Notes
This data set provides measurements of sea ice freeboard and sea ice thickness for the Antarctic region. The data were acquired from the Ice, Cloud, and land Elevation Satellite (ICESat) Geoscience Laser Altimeter System (GLAS) instrument, the Special Sensor Microwave/Imager (SSM/I). The data span thirteen GLAS campaigns, laser 2004 to 2007. Data parameters include sea ice freeboard and sea ice thickness measured in meters. The data at Goddard are provided in three formats: ASCII track data with individual retrieval points, ASCII gridded and interpolated data for each campaign on a 25-km grid, and gridded and interpolated data for each season (FM, MJ, or ON, averaged over all years). The ASCII track data have a resolution of about 175 meters in the along-track direction.

The track data for each individual laser campaign have been averaged for clusters that fall within 50-km square grid cells. Summary statistics of both freeboad and ice thickness are computed. At this time no distribution files are included. At least 250 point values are required within a 50-km cell for the summary to be retained.

Data Processing Notes
Data were processed and calibrated by AWI. Statistical summaries were computed and reformatted by R. Lindsay, PSC from the point data which ranged fro 0.5 to 15 minutes, depending on the mooring.

The summary files have the statistics for

water temperature

instrument depth

sea ice draft.

One mooring, AWI206, has what appear to be a lot of ice bergs (or bad data) with drafts up to 100 m. We have removed any draft greater than 30 m in computing the draft statistics. The uncorrected (for sea level) ULS draft values are included in the point data set but are not included in the summary file. The point data were obtained from http://doi.pangaea.de/10.1594/PANGAEA.785565.

Processing of the CryoSat-2 (PARAMETER) is funded by the German Ministry of Economics Affairs and Energy (grant: 50EE1008) and data from DATE to DATE obtained from http://www.meereisportal.de (grant: REKLIM-2013-04).

Data Processing Notes
This data provides measurements of sea ice thickness and associated uncertainties from the CryoSat-2 mission. Thickness is derived from Radar Altimeter freeboard measurements. The unified thickness data version is derived from the original monthly average AWI products by creating clusters of 50 km averages from the 25 km grid of the AWI source product. Mean ice thickness for each cluster is computed by averaging adjacent grid cells. The input thicknesses are weighted by the random uncertainties provided for each grid cell during averaging (Equation 1). The AWI data sets separates random and systematic uncertainties (see Ricker et al. 2014 for details). Random uncertainties for the unified thickness CDR version of this product are computed from the individual grid cell uncertainties (Equation 2).

Equation 1

Equation 2

Where Tcdris the CDR cluster average thickness, N the number of grid cells from the AWI product used in cluster (4 or 5), Ti is the sea ice thickness for input grid cell, σcdr-random is the random ice thickness uncertainty for the cluster, and σ2i the variance of the random uncertainty in the AWI input product.

Systematic uncertainties are computed as the mean of the input systematic uncertainties.

Regarding the accuracy of the underlying data in the Unified Sea Ice Thickness Climate Data Record: typical RMS errors in the submarine and moored ULS measurements are of the order of 25 cm. (Note: A correction for the first return of the ULS signal has not been applied to any of the ULS data prior to calculating the sea ice draft in the Summary and Distribution files. See Rothrock and Wensnahan (2007) for a discussion of ULS errors). The ICESat freeboard measurements are accurate to within approximately 5 cm, and the current evaluation of the ICESat sea ice thickness error is approximately 50 cm since the thickness is on the order of 10 times the freeboard. If the errors of the point measurements are random, the error in the average draft or thickness is reduced by a factor of 1/sqrt(N), where N is the number of measurements. However, some of the error is not random, and small but significant biases may be present in the aggregate values. The size of these biases is a subject of ongoing research.

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Version History

Table 27. Version History

Version

Date

Description

V1.0

August 2013

Initial release of data set. Data go through April 2012

V1.1

May 2017

Data go through January 2017 and now include Antarctic data

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References and Related Publications

For references specific to each data set used in this CDR, see the Data Acquisition and Processing section for each data set.

JPL's ICESat Sea Ice Thickness and Freeboard Web page: This page provides ICESat sea-ice thickness from JPL. There are ten laser campaigns from 2004 to 2008 in this data set. The fields are smoothed and interpolated to all locations. For the locations and times that correspond to the ICESat1-G (Goddard) data, there are significant differences. The mean difference is approximately 0.5 m thicker for the JPL data. The primary differences in processing between the two data sets are the manner in which open water locations are determined and how snow depth is calculated.

SMOSice: The aim of the SMOSIce study is to develop, improve and validate algorithms for sea-ice thickness retrieval from the 1.4 GHz (L-band, wavelength 20 cm) data of the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission.

The Unified Sea Ice Thickness Climate Data Record project was supported by the NOAA Climate Program Office, Climate Change Data and Detection Program. Distribution of the data set from NSIDC is supported by funding from NOAA's National Environmental Satellite, Data, and Information Service (NESDIS) and the National Geophysical Data Center (NGDC).